Infection And Response
Visão Geral
A single bacterium settling into a warm cut can, in good conditions, split in two every twenty minutes. Thirty divisions later, before a working day is out, one cell has become more than a thousand million. Nothing about your body has changed in those hours except the number of uninvited organisms living inside it, and yet you may go from perfectly well to seriously ill. That is the arithmetic every immune system is built to beat.
This lesson follows that race from both ends. You will see how bacteria and viruses actually make an organism ill, meet the three jobs white blood cells do about it, and find out why recovering from a disease once often protects you for life. Then you will look at the two things people have added to those natural defences, vaccination and antibiotics, and at the uncomfortable reason the second of them is becoming less reliable every decade.
Objetivos
- Microorganisms that cause infectious disease are called pathogens.
- Bacteria and viruses may reproduce rapidly inside the body. Bacteria may produce poisons (toxins) that make us feel ill. Viruses live and reproduce inside cells, causing damage. Knowledge of the structure of viruses is not required.
- White blood cells help to defend against pathogens by: ingesting pathogens (phagocytosis); producing antibodies, which destroy particular bacteria or viruses; producing antitoxins, which counteract the toxins released by the pathogens.
- The immune system of the body produces specific antibodies to kill a particular pathogen. This leads to immunity from that pathogen. In some cases, dead or inactivated pathogens stimulate antibody production. If a large proportion of the population is immune to a pathogen, the spread of the pathogen is very much reduced.
- People can be immunised against a disease by introducing small quantities of dead or inactive forms of the pathogen into the body (vaccination). Vaccines stimulate the white blood cells to produce antibodies that destroy the pathogen. This makes the person immune to future infections by the microorganism, because the body can respond by rapidly making the correct antibody, in the same way as if the person had previously had the disease. The MMR vaccine is used to protect children against measles, mumps and rubella. Details of vaccination schedules and side effects associated with specific vaccines are not required. Students should be able to evaluate the advantages and disadvantages of being vaccinated against a particular disease.
- Antibiotics, such as penicillin, are medicines that help to cure bacterial disease by killing infective bacteria inside the body. It is important that specific bacteria should be treated by specific antibiotics. The use of antibiotics has greatly reduced deaths from infectious bacterial diseases.
- Antibiotics cannot kill viral pathogens. Students should be aware that it is difficult to develop drugs that kill viruses without also damaging the body’s tissues.
- Mutations of pathogens produce new strains. Antibiotics kill individual pathogens of the non-resistant strain but individual resistant pathogens survive and reproduce, so the population of the resistant strain rises. Antibiotics and vaccinations may no longer be effective against a new resistant strain of the pathogen. The new strain will spread rapidly because people are not immune to it and there is no effective treatment. Knowledge of development of resistance in bacteria is limited to the fact that pathogens mutate, producing resistant strains.
- Many strains of bacteria, including MRSA, have developed resistance to antibiotics. Overuse and inappropriate use of antibiotics has increased the rate of development of antibiotic-resistant strains of bacteria. Antibiotics are not currently used to treat non-serious infections such as mild throat infections, in order to slow down the rate of development of resistant strains.
- The development of antibiotic-resistant strains of bacteria necessitates the development of new antibiotics. Required practical: Investigate the effect of disinfectants and antibiotics on uncontaminated cultures of microorganisms.
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- Which statement best describes a pathogen? A. Any microorganism found inside the human body B. A microorganism that causes an infectious disease C. A white blood cell that ingests bacteria D. A poison released by a bacterium Answer: B
- Which of these is NOT a way in which white blood cells defend the body? A. Ingesting pathogens by phagocytosis B. Producing antibodies C. Producing antitoxins D. Producing toxins that destroy body tissue Answer: D
- A patient has influenza, which is caused by a virus. Why would an antibiotic not help? A. Antibiotics only work on toxins B. Antibiotics kill bacteria and have no effect on viruses C. Antibiotics only work if the patient is already immune D. Antibiotics destroy antibodies Answer: B
- A bacterium divides once every 30 minutes. Starting with 4 bacteria, how many are present after 3 hours if none die? A. 24 B. 64 C. 256 D. 512 Answer: C
- Why does the population of an antibiotic-resistant strain of bacteria increase when the antibiotic is used? A. The antibiotic causes the bacteria to mutate B. The bacteria learn to survive the antibiotic C. Resistant individuals survive the antibiotic and reproduce D. The antibiotic is destroyed by the bacteria before it acts Answer: C
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